Ink jet printing systems are one example of digitally controlled liquid emission devices. Ink jet printing systems are typically categorized as either drop-on-demand printing systems or continuous printing systems.
Until recently, conventional continuous ink jet techniques all utilized, in one form or another, electrostatic charging tunnels that were placed close to the point where the drops are formed in a stream. In the tunnels, individual drops may be charged selectively. The selected drops are charged and deflected downstream by the presence of deflector plates that have a large potential difference between them. A gutter (sometimes referred to as a “catcher”) is normally used to intercept the charged drops and establish a non-print mode, while the uncharged drops are free to strike the recording medium in a print mode as the ink stream is thereby deflected, between the “non-print” mode and the “print” mode.
U.S. Pat. No. 6,079,821, issued to Chwalek et al., Jun. 27, 2000, discloses an apparatus for controlling ink in a continuous ink jet printer. The apparatus includes a source of pressurized ink communicating with an ink delivery channel. A nozzle bore opens into the ink delivery channel to establish a continuous flow of ink in a stream with the nozzle bore defining a nozzle bore perimeter. A heater causes the stream to break up into a plurality of droplets at a position spaced from the nozzle bore. The heater has a selectively-actuated section associated with only a portion of the nozzle bore perimeter such that actuation of the heater section produces an asymmetric application of heat to the stream to control the direction of the stream between a print direction and a non-print direction.
U.S. Pat. Nos. 6,554,410 and 6,588,888, both of which issued to Jeanmaire et al., on Apr. 29, 2003 and Jul. 8, 2003, respectively, disclose continuous ink jet printing systems which use a gas flow to control the direction of the ink stream between a print direction and a non-print direction. Controlling the ink stream with a gas flow reduces the amount of energy consumed by the printing system.
Drop-on-demand printing systems incorporating a heater in some aspect of the drop forming mechanism are known. Often referred to as “bubble jet drop ejectors”, these mechanisms include a resistive heating element(s) that, when actuated (for example, by applying an electric current to the resistive heating element(s)), vaporize a portion of a liquid contained in a liquid chamber creating a vapor bubble. As the vapor bubble expands, liquid in the liquid chamber is expelled through a nozzle orifice. When the mechanism is de-actuated (for example, by removing the electric current to the resistive heating element(s)), the vapor bubble collapses allowing the liquid chamber to refill with liquid.
U.S. Pat. No. 6,460,961 B2, issued to Lee et al., on Oct. 8, 2002, discloses resistive heating elements that, when actuated, form a vapor bubble (or “virtual” ink chamber) around a nozzle orifice to eject ink through the nozzle orifice. However, these types of liquid emitting devices have nozzle orifices that share a common ink chamber. As such, adjacent nozzle orifices are susceptible to nozzle cross talk when corresponding resistive heating elements are actuated.
Attempts have been made to reduce nozzle cross talk. For example, U.S. Pat. No. 6,439,691 B1, issued to Lee et al., on Aug. 27, 2002, positions barriers at various locations in the common ink chamber. This, however, increases the complexity associated with manufacturing the liquid emitting device because the common ink chamber is maintained. U.S. Pat. Nos. 6,102,530 and 6,273,553, issued to Kim et al., on Aug. 15, 2000, and Aug. 14, 2001, respectively, also attempt to reduce nozzle cross talk by offsetting each nozzle orifice relative to the common ink chamber. Doing this, however, provides only one refill port necessary to refill the portion of the ink chamber located under the nozzle orifice. Having only one refill port can reduce overall speeds associated with ejecting the liquid because the time associated with chamber refill is increased.